Military combat marks the brain

A single four-month deployment to Afghanistan is associated with brain changes and diminished attention, Dutch scientists report. Most changes went away a year and a half after returning from combat, suggesting that the brain can largely heal itself — and that longer breaks between combat tours might be a good idea.

The study, which focused on healthy Dutch soldiers, reveals how the brain responds to stress outside of a laboratory, says clinical neuroscientist Rajita Sinha of the Yale University School of Medicine. “It’s a nice way to start looking at natural high levels of stress we experience as humans,” she says.

Although the soldiers came back mentally and physically healthy, in Afghanistan they had fought, come under enemy fire and seen their fellow soldiers and civilians wounded or dead.

Researchers led by Guido van Wingen of the University of Amsterdam conducted brain scans while the soldiers performed a lab test that required them to hold several numbers in their memory simultaneously. Initially, the researchers found no brain differences between 33 soldiers who were about to be deployed for the first time and 26 who were still in training. Nor were there differences in a lab task that required intense concentration for several minutes. But the story changed after some soldiers experienced combat, the team reports online September 4 in the Proceedings of the National Academy of Sciences.

After their return, the soldiers went back to the lab for another round of brain scans. During the memory task, the post-deployment brain scans showed lower activity in the midbrain, a region known to be involved in working memory, compared with the brains before deployment.

What’s more, midbrain tissue showed signs of damage and weaker connections with another brain region, the prefrontal cortex. Together, the midbrain and prefrontal cortex are involved in working memory and attention, among other things.

Performance of soldiers who had experienced combat worsened on the attention task, which required participants to quickly and accurately identify groups of dots. After combat, soldiers made more errors. And the number of errors corresponded to some of the changes picked up by the brain scans — the bigger the brain change, the worse the performance.

But most of these brain changes were not permanent, the team found. A year and a half later, all the measurements except for one — the strength of the connection from the midbrain to the prefrontal cortex — had reverted to what they were before combat. “That was quite striking,” says van Wingen. “The brain was able to recover from the adverse effects of stress.”

It’s not clear what a weakened midbrain-to-prefrontal cortex connection means, but it could render a person more susceptible to future stressors, van Wingen says. That result, along with the finding that the brain can reverse the changes given enough time to recover, may mean that soldiers ought to have longer periods of time between deployments, he says. Multiple stressful deployments in quick succession may prevent recovery.